Conventionally, in a radio communication system, a radio communication terminal (a mobile phone terminal, for example) receives base station reference signals (pilot signals or the like, for example) from multiple radio base stations, and is accommodated in a radio base station having the strongest received power of the base station reference signal.
In addition, the radio communication terminal is configured to be handed over, when moving, to a radio base station with the strongest received power of the base station reference signal among radio base stations in the periphery, on the basis of peripheral radio station information acquired from a radio base station in which the radio communication terminal is currently accommodated (Patent Document 1, for example).
In such the conventional radio communication system, an entirely-covered service area is provided by locating a radio base station forming a small cell (a small cell base station, below) adjacent to a radio base station (a large cell base station, below) forming a cell (a large cell, below) larger than the small cell.
With reference to FIG. 1, description will be provided for an example of a case where the radio communication terminal moves at high speed in such conventional radio communication system.
As shown in FIG. 1, a radio communication terminal 10 located at a point P01 in a small cell SC1 is accommodated in a small cell base station 21a with the strongest received power of the base station reference signal. Then, as moving in a direction A, the radio communication terminal 10 is handed over from the small cell base station 21a to a large cell base station 22a, at a point P02 where the received power of the base station reference signal from the large cell base station 22a becomes strongest.
Similarly, as moving in the direction A, the radio communication terminal 10 sequentially is handed over from the large cell base station 22a to a small cell base station 21b at a point P03, from the small cell base station 21b to a large cell base station 22b at a point P04, and from the large cell base station 22b to a small cell base station 21c at a point P05.
Additionally, in order to implement space division multiple access (SDMA) technology, an adaptive array antenna technology for radiating directional beams has been applied to each of the small cell base stations 21a, 21b, 21c and the large cell base stations 22a, 22b, the directional beams changing its directionality dynamically. In the adaptive array antenna technology, the small cell base stations 21a to 21c and the large cell base stations 22a to 22b radiate directional beams by tracking the move of the radio communication terminal 10.
In this way, in the conventional radio communication system, while moving, the radio communication terminal is handed over to a radio base station with the strongest received power of the base station reference signal. In addition, the radio base station stabilizes communication quality by radiating directional beams so that the beams can track the move of the radio communication terminal.
Patent Document 1: JP-A 2005-347906